The present invention relates to a method of and to an apparatus for altering the moisture content of running webs of textile or like material. More particularly, the invention relates to a method and to an apparatus wherein the web which carries a certain amount of moisture is caused to advance through the nip of two cooperating squeezing rollers at least one of which is deformable so as to allow for changes in the width of the nip.
It is known to advance a web of moisture-containing textile or other material through the nip of two squeezing rollers one of which is elastically deformable so that it allows for changes in the width of selected portions of the nip and to thereby change the moisture content of the corresponding portions of the running web. As a rule, the deformable squeezing roller comprises a stationary carrier in the form of a shaft or beam which is surrounded by a deformable rotary shell the external surface of which defines one side of the nip. The space between the shell and the carrier contains at least one row of elastically deformable inflatable cushions which are connectable to a source of compressed fluid, particularly air, so as to deform the corresponding portions of the shell in response to changes of pressure in selected cushions. It is further known to provide the deformable roll with a second set of cushions which are disposed opposite the first set of cushions and can be inflated to move the shell away from the other roller, i.e., to increase the width of the nip. The pressure in the cushions is regulated in dependency upon the moisture content of the corresponding longitudinally extending portions of the running web. As a rule, the moisture content of different portions of the running web is monitored by suitable sensors, and the thus obtained signals are compared with reference signals denoting the desired or optimum moisture content for the respective longitudinally extending portions of the web. The differences between the signals denoting the actual moisture content and the corresponding reference values are utilized to alter the pressure in the corresponding cushions of the first and/or second set so as to increase the moisture content by moving the deformable squeezing roller away from the other squeezing roller or to reduce the moisture content by moving portions of or the entire deformable squeezing roller toward the other squeezing roller.
Squeezing rollers of the above outlined character are used in many types of padders, squeezers and similar machines. Reference may be had to the brochure entitled "BICO-FLEX" D 84.624.1 of Kleinewefers Textilmashinen GmbH. The brochure describes an apparatus wherein the deformable squeezing roller comprises a first set of three inflatable cushions adjacent the nip and distributed in the longitudinal direction of the deformable roller, and two additional inflatable cushions which constitute the second set and each of which is adjacent an end portion of the deformable shell. When the cushions of the second set are inflated, they pull the shell away from the other squeezing roller. On the other hand, when the cushions of the first set arm inflated, or when the pressure in such cushions is increased, the inflated or pressurized cushions of the first set tend to reduce the width of the nip and to thereby reduce the moisture content of the running web. If the web is sufficiently wide to extend all the way between the end portions of the deformable shell, all three inflatable cushions of the first set are filled with a compressed gas so as to exert a pressure along the full width of the running web. However, if the width of the web is less than the axial length of the deformable shell, compressed gas is admitted only into the two outer cushions of the first set so as to prevent excessive squeezing of the marginal portions of the relatively narrow web.
It was already proposed to automate the operation of the just described apparatus by automatically altering the pressure in selected cushions of the first and/or second set. To this end, the running web is monitored downstream of the nip so as to ascertain the moisture content of its marginal portions and of its central portion. The apparatus further comprises a circuit which compares the actual values of the moisture content in the three moinitored portions of the web with preselected optimum or desirable values, and the pressure in the cushions is regulated in dependency upon deviations of the monitored moisture content from the desired or optimum values.